1. Technical Field of the Invention
This invention relates generally to wireless communication systems and more particularly to radio frequency (RF) transceivers that operate in such systems.
2. Description of Related Art
Communication systems are known to support wireless and wire lined communications between wireless and/or wire lined communication devices. Such communication systems range from national and/or international cellular telephone systems to the Internet to point-to-point in-home wireless networks to radio frequency identification (RFID) systems. Each type of communication system is constructed, and hence operates, in accordance with one or more communication standards. For instance, wireless communication systems may operate in accordance with one or more standards including, but not limited to, RFID, IEEE 802.11, Bluetooth, advanced mobile phone services (AMPS), digital AMPS, global system for mobile communications (GSM), code division multiple access (CDMA), local multi-point distribution systems (LMDS), multi-channel-multi-point distribution systems (MMDS), and/or variations thereof.
Depending on the type of wireless communication system, a wireless communication device, such as a cellular telephone, two-way radio, personal digital assistant (PDA), personal computer (PC), laptop computer, home entertainment equipment, RFID reader, RFID tag, et cetera communicates directly or indirectly with other wireless communication devices. For direct communications (also known as point-to-point communications), the participating wireless communication devices tune their receivers and transmitters to the same channel or channels (e.g., one of the plurality of radio frequency (RF) carriers of the wireless communication system) and communicate over that channel(s). For indirect wireless communications, each wireless communication device communicates directly with an associated base station (e.g., for cellular services) and/or an associated access point (e.g., for an in-home or in-building wireless network) via an assigned channel. To complete a communication connection between the wireless communication devices, the associated base stations and/or associated access points communicate with each other directly, via a system controller, via the public switch telephone network, via the Internet, and/or via some other wide area network.
For each wireless communication device to participate in wireless communications, it includes a built-in radio transceiver (i.e., receiver and transmitter) or is coupled to an associated radio transceiver (e.g., a station for in-home and/or in-building wireless communication networks, RF modem, etc.). As is known, the receiver is coupled to the antenna and includes a low noise amplifier, one or more intermediate frequency stages, a filtering stage, and a data recovery stage. The low noise amplifier receives inbound RF signals via the antenna and amplifies then. The one or more intermediate frequency stages mix the amplified RF signals with one or more local oscillations to convert the amplified RF signal into baseband signals or intermediate frequency (IF) signals. The filtering stage filters the baseband signals or the IF signals to attenuate unwanted out of band signals to produce filtered signals. The data recovery stage recovers raw data from the filtered signals in accordance with the particular wireless communication standard.
As is also known, the transmitter includes a data modulation stage, one or more intermediate frequency stages, and a power amplifier. The data modulation stage converts raw data into baseband signals in accordance with a particular wireless communication standard. The one or more intermediate frequency stages mix the baseband signals with one or more local oscillations to produce RF signals. The power amplifier amplifies the RF signals prior to transmission via an antenna.
In many radio transceiver applications, the transceiver operates in a full duplex module (i.e., capable of transmitting and receiving at the same time). Typically, the transmitter transmits on one carrier frequency in a given frequency band (e.g., 900 MHz, 1800 MHz, 1900 MHz, 2100 MHz, 2.4 GHz, 5 GHz, etc.) and the receiver receives on another carrier frequency in the frequency band. Despite using different frequencies, the signal strength of the transmitted signal is significantly greater than that of the received signal (e.g., by as much as 100 dB). As such, the receiver is susceptible to interference from the transmitted signal. To contain the interference, transceivers include a blocking circuit. There are numerous forms of blocking circuits, including duplexer, which can provide 50-60 dB of isolation between the transmitter and receiver. Duplexers, however, contain rather large inductors and capacitors, which requires them to be implemented off-chip from the transceiver. Other types of blocking circuits may have issues locking on to the blocking signal (i.e., the signal transmitted by the transmitter as received by the receiver).
Therefore, a need exists for a blocking circuit that can lock on to and substantially attenuate the blocking signal.